1. Field of the Invention
The present invention relates to a printed wiring board having a thin profile while maintaining sufficient flatness, and associated manufacturing methodology.
2. Background Art
With recent advancements toward high-function electronic equipment, there has been an increasing demand for smaller and thinner products. Along with rapid advancements in high-density integration of electronic parts such as IC chips and LSI used for such electronic equipment, there has been a need to further increase the wiring density of package substrates (hereinafter referred to as “PKG substrate”) for loading these electronic parts to achieve smaller and thinner profiles.
Typically, these PKG substrates employ a reinforced member, such as a glass-fabric copper-clad laminate as a core substrate, and have a configuration in which a buildup layer is formed in both top and bottom surfaces of the core substrate. A through-hole on the core substrate is formed to interconnect the buildup layers of both surfaces. The diameter of these through-holes, or vias, determine the circuit density (i.e. how closely circuit wires may be placed in relation to each other) that can be achieved on the PKG substrates. The smallest possible diameter of the through-holes is determined at least by the core substrate.
To reduce through-hole diameter, a multilayer printed wiring board without a core substrate has been proposed. In one conventional example a multilayer printed wiring board (hereinafter referred to as “conventional example”) is manufactured by laminating an interlayer material and a conductor layer alternately on a metallic foil surface on a support substrate to form a buildup layer. Then a predefined portion from the circumference of the buildup layer is removed, and the support substrate and the buildup layer are separated so that the metallic foil remains on both the buildup layer and the support substrate. The remaining metallic foil on the buildup layer is etched to form a BGA pad. Japanese Unexamined Patent Application Publication 2006-19591, the entire contents of which is incorporated herein, provides one such conventional example.